1. Field of the Invention
The present invention relates to methods for fabricating cores for light guide plates used in liquid crystal display (LCD) devices, and more particularly to a method for fabricating a core that has concentric double-circle patterns.
2. Description of Prior Art
A liquid crystal display is capable of displaying a clear and sharp image through millions of pixels of image elements. It has thus been applied to various electronic equipment in which messages or pictures need to be displayed, such as mobile phones and notebook computers. However, liquid crystals in the liquid crystal display do not themselves emit light. Rather, the liquid crystals have to be lit up by a light source so as to clearly and sharply display text and images. The light source may be ambient light, or part of a backlight system attached to the liquid crystal display.
A conventional backlight system generally comprises a plurality of components, such as a light source, a reflective plate, a light guide plate, a diffusion plate and a prism layer. Among these components, it is generally believed that the light guide plate is the most crucial component in determining the performance of the backlight system. The light guide plate serves as an instrument for receiving light beams from the light source, and for evenly distributing the light beams over the entire light guide plate through reflection and diffusion. In order to keep light evenly distributed over an entire surface of the associated liquid crystal display, the diffusion plate is generally arranged on top of the light guide plate.
FIGS. 7-12 show successive stages in a conventional method for fabricating a patterned core for a light guide plate, the core having concentric double-circle patterns. The method includes the following steps:
Referring to FIGS. 7 and 8, the initial steps are: providing a substrate 100, and coating a uniform photo-resist layer 200 on the substrate 100; exposing the photo-resist layer 200 using a photo-mask 300, the photo-mask 300 having a plurality of circular transparent areas 320 and a light shielding area 340; and performing a developing step in order to transfer the pattern of the photo-mask 300 onto the substrate 100. These initial steps result in a remaining photo-resist area 240 being retained on the substrate 100. The substrate 100 defines circular exposed portions 220 that are not covered by the remaining photo-resist area 240.
FIG. 9 shows the substrate 100 after a first etching step has been performed. Etchant reacts with the exposed portions 220 of the substrate 100 to form large circles 120 of the concentric double-circle patterns. Each large circle 120 has a surface 122.
As indicated in FIGS. 10 and 11, a second photo-resist layer 200 is coated on the substrate 100 including the surfaces 122 of the large circles 120. A photo-mask 400 is provided for use in a second exposing step. The photo-mask 400 includes a plurality of annular transparent areas 420. A light shielding area 440 is defined within each transparent area 420. The remainder of the photo-mask 400 not including the transparent areas 420 and the light shielding areas 440 is defined as a light shielding area 460. Light beams pass through the transparent areas 420 toward the substrate 100. Exposed portions of the remaining photo-resist area 240 that is on the surfaces 122 react accordingly. A second developing step is then performed, in order to transfer the pattern of the photo-mask 400 onto the substrate 100. This results in a remaining photo-resist area 124 being retained on the surface 122 of each large circle 120.
FIG. 12 shows the substrate 100 after etchant has reacted with exposed portions of the large circles 120.
Finally, a photo-resist denuding step is performed to eliminate the remaining photo-resist areas 124, 240. The core with concentric double-circle patterns is thus provided.
However, the above-described conventional method requires two etching steps. Moreover, a precise orientation is necessary when the second exposure step is performed. These requirements make the process unduly complicated and time-consuming, resulting in high operating costs and low productivity.